Adhesive compositions and composite materials

ABSTRACT

A composite material is formed from a flexible porous hardening foam (e.g. polyurethane) and an adhesive composition which sets to a water-resistant film and contains a water-absorbent filler (e.g. fumed silica) in an amount such that the film is water absorbent. The adhesive reinforces the foam while preserving its porosity and absorbency. The material is suitable for shoe insoles and handgrips. The adhesive may be primarily in a surface layer e.g. of cloth ( 14 ) applied to the foam ( 12 ); or the foam ( 22 ) may be saturated with the composition prior to curing.

The present invention relates to adhesive compositions and to compositematerials made from such adhesive compositions and solid foam materials.In further aspects it relates to methods of making such compositematerials, and articles made from them. The invention is primarilyconcerned with composite materials which are porous, resilientlycompressible, and water resistant. Such materials may be particularlysuitable for the manufacture of insoles and handgrips (e.g. for sportsrackets).

The most widely used solid foam materials are polyurethane foams. As iswell known, these can be produced with a wide range of rigidity (fromvery soft to rigid) and a wide range of density. A further variable iswhether the material is open-cell (and hence porous) or closed cell.

Low density flexible polyurethane foams are materials of density 10-80kg/m³, composed of lightly cross-linked open cells. Air can flow easilythrough them. They are soft, with little strength or resistance toabrasion. Their net-like surface layers make it difficult to bond themto other articles, e.g. for lamination. They are typically used ascushioning, in bedding or upholstery. In contrast, polyurethane foammaterials conventionally used for shoe soling and the like aremicrocellular foams (i.e. denser than “high density foams”), withintermediate softness. Such materials have little if any porosity. Theyare generally self-skinning, which further reduces any porosity they mayhave. Thus they typically have to be needled if they are required to bebreathable.

In one aspect the present invention enables one to reinforce a lowdensity flexible foam while preserving substantial porosity. Use is makeof a water-resistant, water-transmissive glue. This may be based on aglue which is not substantially water-transmissive, typically alatex-type adhesive, in which a water-absorbent filler has beenincorporated so that a film formed from the adhesive is water absorbent.

It is known to incorporate fillers, including water-absorbent fillers,in adhesive compositions. However they are incorporated at low levels(e.g. ¼-1% w/w) and do not confer water-absorbance.

Thus in a first aspect the invention provides a composite materialformed from a low density flexible plastics foam material (preferably10-80 kg/m³) and an adhesive composition comprising a water-resistantglue composition and a water-absorbent filler, the filler beingincorporated in an amount sufficient to confer water absorbance on afilm formed from the adhesive composition. The foam material willgenerally be porous, and the composite material desirably retainssubstantial porosity.

Generally the glue composition is a latex e.g. astyrene-butadiene-rubber (“SBR”) latex (preferably carboxylated) or adispersion based on polyurethane or acrylonitrile-butadiene or acrylicsor ethylene-vinyl acetate (EVA) or copolymers or terpolymers based onany of these. Generally it will be settable or curable to a non-tackystate. That is, it is not a pressure-sensitive adhesive as used on‘self-adhesive’ articles such as labels and tapes. Neither is it aremoist adhesive (as used on stamps etc.)

The glass transition temperature of the glue composition may be 10-15°(or lower if intended for low temperature use, e.g. 0° or less).

The amount of filler is preferably 5-7% of the adhesive compositions(w/w). Suitable fillers are inorganic materials of small particle size(e.g. <5 μm, preferably <1 μm.). Silica, particularly fumed silica, iscurrently preferred. Calcium carbonate is also usable.

The adhesive composition may be formed by mixing components A and B inapproximately equal amounts by weight (e.g. 40-60% of A, 60-40% of B),where:

Component A is a latex of solid content 40-55% by weight (preferably acarboxylated SBR latex); and

Component B comprises water (86-90 parts) and filler (preferably silicasuch as Aerosil 200) (10-14 parts). It may further include a bactericide(1-2 parts). (All parts are by weight.)

The compounded adhesive may also include a crosslinker which is reactivewith carboxy and hydroxy groups, e.g. a polyfunctional aziridine such astrimethylolpropane-tris-(β-(N-aziridinyl) propionate (available asXAMA-2 from EIT Inc), or CX-100 (Zeneca Resins). Use of 0.5-2% w/w ofsuch a trifunctional linker can improve the water- andchemical-resistance and bond strength of the adhesive.

Alternative adhesive compositions which may be used are breathableadhesives or coatings. Their ‘breathability’ may be due to theirmolecular structure and is generally not dependent on fillers. Knownexamples include water-based polyurethane products such as Witcoflex 120and 130 (Baxenden Chemicals). These provide water-resistant, breathable,hydrophilic coatings. However they are relatively expensive. Furthermorethey tend to be too soft for various applications such as insoles.

The plastics foam material is preferably a polyurethane foam. (Otherpossibilities included polyethylene.) Its density is preferably 10-60kg/m³, more preferably 20-60, still more preferably 30-50 and mostpreferably 40-45 kg/m³. It is desirably a flexible, fully open,sponge-like material. It is generally 3-12 mm thick. For use inproducing insoles for normal use, thicknesses in the range 4-6 mm arepreferred. Insoles for sports shoes may be up to 10 mm or more. Materialfor handgrips may be 3 mm thick. (Thinner foam is not readilyavailable.)

The adhesive is preferably a filler—containing adhesive as describedabove or, less preferably, a breathable adhesive.

In a second aspect the invention provides an adhesive compositioncomprising a water resistant glue composition which is a latex or otheraqueous polymer dispersion and, as a filler, fumed silica incorporatedin an amount such that a film formed from the adhesive composition iswater absorbent (said composition setting or curing to a non-tackystate).

In a third aspect the invention provides an insole comprising acomposite material according to the first aspect.

In a fourth aspect the invention provides a handgrip (e.g. for a sportsracket or hand tool) comprising a composite material according to thefirst aspect.

In further aspects the invention provides methods of producing compositematerials according to the first aspect or articles according to thethird or fourth aspect; and a method of producing or repairing ahandgrip, optionally in situ on a handle. Application of a coating of anadhesive composition as used in the present invention to a foam-basedhandgrip, or a foam substrate for use in forming a handgrip, leads to ahandgrip of enhanced durability. The filler in the adhesive compositioncan provide durability and good nonslip properties, as well as ensuringthat the set adhesive is able to absorb moisture.

In one type of embodiment, the adhesive composition is primarily presentin a fabric layer which is adhered thereby to a major surface of thefoam material. Preferably the foam material is in the form of a sheet,and said fabric layers are adhered to both major surfaces. This gives aproduct which is reversible and washable. Preferably the fabric wassoaked in the adhesive composition and the setting thereof both adheredthe fabric to the foam material and provided the fabric with aprotective coat. The fabric is preferably of a water-absorbent material,e.g. based on cotton (e.g. pure cotton or cotton-polyester or otherknown blend).

The fabric may be woven (cloth) or nonwoven. Suitable nonwovens includehighly porous materials, composed of fibres of synthetic polymermaterials.

In a second type of embodiment, the plastics foam material was saturatedwith the adhesive composition which was subsequently cured to produce areinforced foam material. This type of embodiment generally does nothave the cloth surface layer(s). The plastics foam is preferably ofthickness 4 or 5-12 mm.

A preferred method of producing the first type of embodiment comprisesthe following steps: (a) fabric is soaked with the adhesive composition(suitably by immersion); (b) the soaked fabric is applied to the foammaterial and the assembly is oriented so that the fabric is on theunderside; and then (c) heat is applied to the fabric, preferably usinga jet of hot gas or infra red irradiation. The orientation of theassembly reduces the penetration of the adhesive composition into thefoam material.

For insoles, the foam is typically about 5 mm thick and is preferably30-40 kg/m³. It may be reinforced either by the adhesion of a fabriclayer to one or both faces, or by the saturation method referred toabove.

For handgrips, a foam layer about 3 mm thick is preferred, andreinforcement is preferably by adhesion of a fabric layer. For providinga protective coating on a handgrip, it is preferred to use an adhesivecomposition according to this invention, particularly one based on apolyurethane dispersion with fumed silica as filler.

The following table compares the properties of various materials forforming insoles. “Present invention” refers to preferred embodiments ofthe present invention of the type consisting of polyurethane foam withcloth bonded to both faces. The adhesive used is based on a carboxy SBRlatex containing silica. The cloth was saturated with the latexcomposition which thus provided surface protection for the cloth as wellas bonding it to the foam.

Present Invention High (6/10 mm Self-skinning Cloth Laminated Leather,Compressible Polyurethane Foam on Rubber Optionally Foam Resilient toModerate Moderate Backed Compressibility 2/2.5-3 mm) (3 mm compressibleto 1.5-2 mm) Moderate Water Absorbance 400-500% 300% 300% 300% (W/W) AirFlow High Poor unless perforated after Reasonable Efficiency formationDurability High High Moderate/Low High Reversibility Yes No No Yes (notif foam-backed) Washability Washable Rinsable Rinsable Washable withdetergent Cost Low Low Low High

Some embodiments of the invention will now be described with referenceto the accompanying drawings in which:

FIG. 1 is a schematic sectional view of a composite material which is afirst embodiment of the invention;

FIG. 2 is a like view of a second embodiment.

The composite material 10 shown in FIG. 1 has a core of flexible, fullyopen-celled polyurethane sponge 12, of thickness 6 mm. The raw materialhad a density of 40 kg/m³. Each of the major faces carries a layer 14 ofwoven cotton cloth. Prior to application, the cloth was soaked with anadhesive composition (to be described later). This has soaked a smallway into the foam material 12 (shown as surface layer 16). Additionally,it provides surface coating layers 18 on the outer faces of the cloth.

The adhesive composition was a carboxylated SBR latex having a glasstransition temperature of 10° and a solids content of 50% w/w. Itcontained 6% by weight of a silica filler, namely Aerosil 200(™). Italso contained a bactericide.

In the manufacture of the composite material 10, cloth was cut toprovide pieces for covering the top and bottom faces of the foam. Thecloth pieces were soaked in the adhesive composition. One piece of clothwas removed and laid on the upper surface of the foam composition, whichwas immediately inverted. Hot air was then directed at the exposedsurface of the cloth 14 until the adhesive was cured. Cloth 14 was thenapplied to the upper face of the foam material in the same way.

FIG. 2 shows a cheaper form of composite material. It consists of apiece of polyurethane foam 22 having the same characteristics as thefoam material 12 of the first embodiment, except that it is 10 mm thick.This material was immersed in the same adhesive composition as describedabove, and squeezed so that it became saturated. It was then removed anddried using hot air. The result is a sheet of foam that is stillsubstantially porous, but which is much stronger and more resistant toabrasion than the untreated foam. It is also somewhat more rigid.

The composite materials as shown in FIGS. 1 and 2 may be cut to provideinsoles for other shaped objects. (Alternatively, the foam could be cutbefore the treatment steps but this is not generally convenient). Aninsole (or a hand grip) is desirably porous, to allow absorption ofsweat. It is clearly important that adhesive used in its productionshould not be water soluble. The adhesion composition used herein leadsto an adhesive bond which is highly resistant to water but which isstill water absorbent, due to the high content of an appropriate filler.

What is claimed is:
 1. A porous, resiliently compressible andwater-resistant composite material comprising (i) a layer of open-cellflexible plastic foam material having two oppositely directed majorsurfaces; and (ii) at least one fabric layer overlying a respective oneof said major surfaces of the foam material layer, said fabric layerhaving been soaked in an adhesive composition which comprises acarboxylated SBR latex and 5 to 7%, by weight, of the adhesivecomposition of a water-absorbent filler selected from silica and calciumcarbonate, whereby when the fabric layer is disposed on said majorsurface, the adhesive composition soaks into a surface layer of the foammaterial layer; the adhesive composition being subsequently cured toproduce a composite material wherein the cured adhesive bonds the atleast one fabric layer to the foam material layer and provides aprotective coat on the outer surface of the at least one fabric layer.2. A composite material according to claim 1 including a second fabriclayer adhered to the other of said major surfaces of the foam materiallayer.
 3. A composite material according to claim 2 wherein the plasticsfoam material was saturated with the adhesive composition which wassubsequently cured to produce a reinforced foam material.
 4. A compositematerial according to claim 1 wherein the adhesive composition includesa polyfunctional crosslinker which is reactive with carboxyl andhydroxyl groups.
 5. A composite material according to claim 1 whereinthe filler is fumed silica.
 6. A composition material according to claim1 wherein the adhesive composition includes a bactericide.
 7. Acomposite material according to claim 1 wherein the plastics foammaterial is a polyurethane foam.
 8. A composite material according toclaim 1 wherein the density of the foam material is 10-60 kg/m³.
 9. Acomposite material according to claim 8, wherein the density of the foammaterial is 30-50 kg/m³.
 10. A composite material according to claim 9wherein the density of the foam material is 40-45 kg/m³.
 11. An insolecomprising a composite material according to claim
 1. 12. A handgripcomprising composite material according to claim
 1. 13. A porous,resiliently compressible and water-resistant composite materialcomprising (i) a layer of open-cell flexible plastic foam materialhaving a density of 10 to 80 kg/m³ and having two oppositely directedmajor surfaces; and (ii) at least one fabric layer overlying arespective one of said major surfaces of the foam material layer, saidfabric layer having been soaked in an adhesive composition whichcomprises a carboxylated SBR latex and 5 to 7%, by weight, of theadhesive composition of a water-absorbent filler selected from silicaand calcium carbonate, whereby when the fabric layer is disposed on saidmajor surface, the adhesive composition soaks into a surface layer onlyof the foam material layer; the adhesive composition being subsequentlycured to produce a composite material wherein the cured adhesive bondsthe at least one fabric layer to the foam material layer and provides aprotective coat on the outer surface of the at least one fabric layer.14. A porous, resiliently compressible and water-resistant compositematerial formed from an open-cell flexible plastics foam material havingdensity of 10 to 80 kg/m³ and an adhesive composition comprising acarboxylated SBR latex incorporating a polyfunctional aziridinecrosslinker and a water-absorbent filler selected from silica andcalcium carbonate, the filler being incorporated in an amount of 5 to7%, by weight, of the adhesive composition.